In cast molding methods of producing ophthalmic lenses, such as contact lenses, a reaction mixture or polymerizable lens precursor composition is cured in a lens shaped cavity defined by a first mold member with a concave lens forming surface and a second mold member with a convex lens forming surface, or a female and male mold member, respectively. The mold members are typically produced by injection molding a thermoplastic polymer into mold shaped cavities. Examples of thermoplastic polymers used to make ophthalmic lens molds include non-polar thermoplastic polymers, such as polypropylene, polystyrene, and polyethylene; and polar thermoplastic polymers, such as ethylene-vinyl alcohol copolymers and poly(vinyl alcohol) homopolymers. When cast molding a contact lens, after placing the polymerizable composition in the first mold member, the first and second mold members are placed together or coupled together to form a lens assembly with the lens shaped cavity therebetween. The mold assembly is then cured to polymerize the polymerizable composition, forming the polymerized lens body in the lens shaped cavity of the mold assembly.
Contact lenses, including silicone hydrogel contact lenses, have been cast molded in molds made of ethylene-vinyl alcohol (EVOH) copolymers with high crystalline content (and low amorphous content), for example SOARLITE™ S available from Nippon Gohsei, Ltd., Osaka, Japan. Some EVOH copolymers have levels of crystallinity of about 40% or higher. Molding silicone hydrogel lenses in EVOH molds has been found to result in lenses having ophthalmically acceptably wettable surfaces. Previously, it was necessary to apply a surface treatment such as, for example a plasma treatment, or to include an interpenetrating network of a polymeric wetting agent in silicone hydrogel contact lenses in order for the lens surfaces to be ophthalmically acceptably wettable when hydrated. However, EVOH is an expensive material, which negatively impacts production costs. Molds made of EVOH typically are harder and more brittle than would be ideal, and it can be difficult to release the lens body from the mold members of the mold assembly following curing, which negatively impacts lens yields and costs.
It has also been proposed to use forms of poly(vinyl alcohol) (PVOH), including modified forms of PVOH, to form contact lens molds. While these forms of PVOH appear attractive due to their water solubility, they are not ideal for use as contact lens molds. For example, as the traditional melt processing temperature and thermal degradation temperature of pure PVOH are almost the same, it is very difficult to use these materials to injection mold contact lens molds. While some modified forms of PVOH have been proposed for use as contact lens molds, these modified forms of PVOH still retain some of the undesirable properties of pure PVOH, such as high crystalline content that reduces light transmission through the material, slow dissolution in water at lower temperatures, and portions of the material may not dissolve completely. Further, aqueous solutions of pure or modified PVOH can gel or foam easily, and the materials may produce cloudy aqueous solutions. Although the prospect of a contact lens mold that could be dissolved in water would be attractive, these undesirable properties make it difficult to use pure or modified forms of PVOH in commercial production of contact lenses.
In view of the above, it can be appreciated that a need exists for contact lens molds comprising new types of materials for cast molding ophthalmic lenses including silicone hydrogel contact lenses, new ophthalmic lenses cast molded using molds comprising these new types of materials, and associated manufacturing methods which use less expensive, more process-friendly molding materials. A need exists particularly for materials that can be injection molded in order to form contact lens molds which can be used to cast mold silicone hydrogel contact lenses that has ophthalmically acceptably wettable lens surfaces without application of a surface treatment such as plasma to the lens body, or without the presence of components in the lens forming composition that form an interpenetrating network (IPN) of a wetting agent in the lens body during curing of the lens.
All publications, including patents, published patent applications, scientific or trade publications and the like, cited in this specification are hereby incorporated herein in their entirety.